HED H3 tire blow off

nospam wrote:

Also I'm gonna stop using latex tubes because I feel it is easier for
'tube inclusions' to occur.

I too have noted a great deal of "inclusion difficulty" with certain combinations of tires and latex
tubes. At times I found it extremely difficult to get the latex tubes installed correctly because
they seemed to "stick" to the tire and not "want" to get seated properly inside the tire. Different
amounts of air volume was tried to help form and unform the tubes in the hope the technique would
help -- it was mostly to no avail.

The simplest and most effective way to keep the tubes from sticking in the wrong position
(specifically getting stuck under the tire bead), was to talc the combination before installation.
Then the tubes don't stick to the tire while trying to get them installed. Just note that "talcing
tubes/tires," as an issue, has a religious fervor associated with it. As best I can tell, it rarely
matters one way or the other whether one does or does not do it. That said, in this specific case,
it seemed to greatly help get the tubes seated properly. I have never noted a situation with butyl
tubes where the effect was so strongly pronounced as that with latex tubes. So another way of
"solving the problem" is to only use butyl tubes, as you noted.

On Fri, 14 May 2004 18:39:37 GMT,
wrote:

Carl Fogel writes:

Is this the common scenario, with a hot rim rolling slowly under
no braking to blow the rim off?

Who said anything about "no braking"?????

Why does the pressure rise so dramatically after no further
braking was generating heat? Or would it have blown off anyway in
another few moments if you'd kept descending?

How hot does the rim get and what would the pressure increase be?
Is the original example of 100 psi rising to 120 psi what you
would expect? Would such a rise blow your tires off?

Much more than that.

I still find Kinky's question interesting and still don't know the
answer, so I hope that you'll think it through and come up with a
helpful answer.

"My friend stopped to take pictures so I waited for him riding the
rear brake over the lever hood at less than 10mph when BAM!"

Actually, you never do say which tire went BAM! Some of us would
assume that the front tire is the one that would heat up on a descent.
We weren't there. The lever hood is a nice detail, but you gotta write
more clearly, Jobst. (After all, you were surprised.)

Carl, we are talking about brake heating and tire blow-off resulting
from heating the air in the tire. Descriptions here would get longer
than the unnecessary citation you already include. I see no ambiguity
in what I wrote and anyone following the thread with attention could
deduce that the rear tire was the only one being heated. My surprise
came from the light braking I was doing with a hand draped over the
lever hood while creeping along.

As another example of how easily things may be mis-read, what does the
end of this sentence mean?

" It never occurred to me that this would blow off the tire, having
descended this road many times without incident with many others."

Many others? What others?

Others means other riders on many rides over the Grosse Scheidegg pass
on bicycle tours in the Swiss Alps on the same bicycle with the same
wheels and similar tires over many years in the past. Now what did I
leave out? Oh yes, and descending rapidly and braking hard down the
12+ percent grade with many hairpin turns.

Many other tires? (Well, obviously. Descending without tires would be
tricky.)

Your getting warmer. Keep it up. I guess Jose Rizel's exchange
knocked your comprehension a bit. Don't get so testy.

Other friends? (Seems unlikely, but perhaps the point is that many
other riders had no tire trouble.)

I'm sure you can come up with an even more distantly related scenario.
You are engaging in what appears to be willful misunderstanding.

Other brands of tires? (Possibly, but stretching.)

You know what you meant, of course, but I don't. A single word
would probably clear it up. Or maybe removing the last three words
would still say what you meant. Or it could easily be something
that I haven't guessed. Or even just a word processor editing oops.

Quick writing about vivid events is often like this--we can't believe
that the reader failed to follow us, while they're left wondering what
on earth we meant. You can't imagine how I could think it was your
front tire, while I can't figure out which one you meant.

Well how about explaining why a front tire would blow-off the rim with
only the rear brake applied. If you followed that concept I think you
would come upon the fact that the rear tire came off.

Leaving clarity theory aside, you say that it never occurred to you
that this would blow the tire off. So what's the explanation? I seem
to recall that you've suggested that prolonged low-speed braking is
worse than high-speed descent because there's less air cooling of the
rim, but I may have misunderstood you.

You may have taken from what I wrote that all slow speed braking can
cause tire blow-off yet you suspect my front tire came off. I thought
the heat input to the wheel at such low speeds would not cause
overheating but it reinforced my appreciation for the effects of air
cooling loss at low speeds. This is much like riding next to a friend
who is walking down an RR underpass sidewalk while lost in
conversation. Fortunately such descents are too short but they are
steep enough and at low speeds that we regularly find innocuous, tire
blow-off can occur.

Was this a prolonged low-speed descent? You say that you'd slowed
down for a friend, but for how long? A minute or so? Ten minutes?
A hundred yards, half a mile, a thousand feet of altitude?

For about 200 meters distance. The point is that this example in
particular underscores the heat generated and loss of cooling. That
was the point of mentioning it so others don't believe that slowing
down will prevent this.

And where does the heat generated at the tire's contact patch go on
a long descent with heavy braking? Into the pavement? The tire?
Dissipated into the air? Or am I mistaken about as much heat being
generated at the contact patch as at the brake pad?

There is no perceptible heat at the contact patch. As I mentioned. if
there were, tires would wear out in a short time.
Heat can be derived from the RR tables shown here often:

http://www.terrymorse.com/bike/rolres.html

You can compute the work of pushing a few grams times speed. RR
losses are energy that goes into heat.

Jobst Brandt



Dear Jobst,

If you think that adding the words "front" or "riders" is too much,
Lord knows what else you're leaving out.

It might help people like me (and possibly Kinky) if someone mentioned
that while the temperature of the air inside the tire rises as it's
heated by the hot metal rim against the tube, the hot air itself
inside the tube is neverthelless a very poor thermal conductor and
acts to insulate the bulk of the tire that doesn't touch the rim.

As for the contact patch, perhaps we're still misunderstanding each
other. Those rolling resistance tables that you mention for tires are
for loaded tires rolling freely, aren't they? What I'm wondering about
is tires under the same weight performing heavy, continuous downhill
braking.

Rear tires, I gather, do wear out much faster on climbs, where they're
putting more force into the pavement at lower speeds than when
they're cruising at higher speeds along level pavement. So do tires
performing hard, steady cornering.

I'm wondering about tires used for long, steady, steep downhill
braking. Is there a significant difference between this and unbraked
rolling resistance? That is, do tires wear out sooner under heavy
braking? If they do, do they get hotter than usual? They're not as hot
as the rim, but what heat do they add or remove from the air in the
tube?

Is there any effect on the section of tire pressing against such hot
rims? That is, does it soften and bulge, expand more than the rim,
become brittle and hard?

The inner tube explodes, but come to think of it, I don't know what
actually happens to the tire. Does the bead break? Or does the casing
split above the bead? Or does the tire come off the rim, allowing the
tube to explodes, and yet the tire remains astonishingly usable?

You were there, but I wasn't, so I have to ask.

Carl Fogel

wrote:

The flimsy perforated disks offered today are a mere lacework of thin
steel that is easily deformable at room temperature and easily
collapsible at yellow heat, which it would achieve on descending roads
I have encountered on my rides.

I've had a play on a MTB with discs and a sharp stop on level ground
from only about 15mph made the front disc too hot to touch. There isn't
much heat capacity because the manufacturers have to keep the weight
competitive with rim brakes.

However, I once saw a pair of (heavy looking) touring tandemists who
were solely relying on Hope discs front and rear; the discs were rather
blued by heat but the tandemists were satisfied with their performance
so far. They weren't as drilled-out as the latest MTB types, but I'm
sure they'd still get cherry red on a serious descent. Maybe that's
part of the fun.

Carl Fogel writes:

Lord knows what else you're leaving out.

As I said, the context should make clear who and what did what.

It might help people like me (and possibly Kinky) if someone
mentioned that while the temperature of the air inside the tire
rises as it's heated by the hot metal rim against the tube, the hot
air itself inside the tube is nevertheless a very poor thermal
conductor and acts to insulate the bulk of the tire that doesn't
touch the rim.

....or get perceptibly hot.

As for the contact patch, perhaps we're still misunderstanding each
other. Those rolling resistance tables that you mention for tires
are for loaded tires rolling freely, aren't they? What I'm
wondering about is tires under the same weight performing heavy,
continuous downhill braking.

As I said, if there were a lot of skidding taking place, tires would
wear out in a short time. In my case, front tires wear out about half
as fast as rear tires. Neither of these tires get hot from road
contact, braking or not, and tread and casing (and tubes) insulate any
heat generated from inflation air enough to make that no issue. That
is why I suggested you feel how hot rims get from braking and you'll
notice that the tire is not noticeably warm.

Rear tires, I gather, do wear out much faster on climbs, where
they're putting more force into the pavement at lower speeds than
when they're cruising at higher speeds along level pavement. So do
tires performing hard, steady cornering.

Next time you climb a steep forested hill, stop and feel the tire and
you'll have your answer. I have had flats under such circumstances
and noted that the tire was essentially ambient temperature, not hot
from traction as you suspect.

I'm wondering about tires used for long, steady, steep downhill
braking. Is there a significant difference between this and
unbraked rolling resistance? That is, do tires wear out sooner
under heavy braking? If they do, do they get hotter than usual?
They're not as hot as the rim, but what heat do they add or remove
from the air in the tube?

Herring season is over around here, red or otherwise. This seems to
be a meaningless pursuit to change the subject. Forget about road
friction as a heater. Even RR, which is a constant with tires up,
down, or on the level is important for performance but insignificant
as a heat source.

Is there any effect on the section of tire pressing against such hot
rims? That is, does it soften and bulge, expand more than the rim,
become brittle and hard?

Not that I can discern. Judging from tube inclusion blowouts, they
are also not temperature related but are caused by an unseated bead.

The inner tube explodes, but come to think of it, I don't know what
actually happens to the tire. Does the bead break? Or does the casing
split above the bead? Or does the tire come off the rim, allowing the
tube to explodes, and yet the tire remains astonishingly usable?

Carl, you have suddenly become so un-resourceful. Answers to these
questions are contained in this thread and in the FAQ:

http://draco.acs.uci.edu/rbfaq/FAQ/8b.4.html

You were there, but I wasn't, so I have to ask.

You read it but didn't comprehend.

Jobst Brandt

wrote in message
...
Jay Beattie writes:

Sounds like an argument for disk brakes.

Interesting that you bring that up. I am unwilling to load my
bicycle
with the extra weight and complexity to try it but I have
considered
the heat I have observed. I cannot imagine that the typical
disc we
see on bicycles today, weighing only a few 100 grams, can
absorb the
energy required without collapsing and initiating brake
failure. A
crumpled disk is a certain endo that I am unwilling to test,
even if I
were offered such a bicycle before a descent.

The flimsy perforated disks offered today are a mere lacework
of thin
steel that is easily deformable at room temperature and easily
collapsible at yellow heat, which it would achieve on
descending roads
I have encountered on my rides.

In the summer:

http://tinyurl.com/pd86

The Stelvio is grand, but my favorite picture is that one of
Tende pass -- the one shot from the top, where the switch-backs
look like a mountain of large intestines. That's gotta be hard on
brakes. -- Jay Beattie.

Jay Beattie writes:

Sounds like an argument for disk brakes.

Interesting that you bring that up. I am unwilling to load my
bicycle with the extra weight and complexity to try it but I have
considered the heat I have observed. I cannot imagine that the
typical disc we see on bicycles today, weighing only a few 100
grams, can absorb the energy required without collapsing and
initiating brake failure. A crumpled disk is a certain endo that I
am unwilling to test, even if I were offered such a bicycle before
a descent.


The flimsy perforated disks offered today are a mere lacework of
thin steel that is easily deformable at room temperature and easily
collapsible at yellow heat, which it would achieve on descending
roads I have encountered on my rides.

http://tinyurl.com/pd86

The Stelvio is grand, but my favorite picture is that one of Tende
pass -- the one shot from the top, where the switch-backs look like
a mountain of large intestines. That's gotta be hard on brakes.

The Stelvio is a pass with unforgiving hairpin turns, most of which
would result in a fatal fall on brake failure. The Tende, in
contrast, is a rough and unpaved 19th century road with no such
exposure. To make up for that it has plenty of esses that require low
speed braking that generates plenty of heat.

Jobst Brandt

Zog The Undeniable wrote:

wrote:

The flimsy perforated disks offered today are a mere lacework of thin
steel that is easily deformable at room temperature and easily
collapsible at yellow heat, which it would achieve on descending roads
I have encountered on my rides.

I've had a play on a MTB with discs and a sharp stop on level ground
from only about 15mph made the front disc too hot to touch. There isn't
much heat capacity because the manufacturers have to keep the weight
competitive with rim brakes.

However, I once saw a pair of (heavy looking) touring tandemists who
were solely relying on Hope discs front and rear; the discs were rather
blued by heat but the tandemists were satisfied with their performance
so far. They weren't as drilled-out as the latest MTB types, but I'm
sure they'd still get cherry red on a serious descent. Maybe that's
part of the fun.

Tandemists who follow consumer trends are already adopting disks. The
best setup would be double discs, as this would reduce, practically to
zero, torque caused by a solitary disk. And of course a double would
result in a much larger heat capacity.

I have seen a Phil Wood double-disk front hub, but I can't provide a Web
reference. Cost? "If you have to ask. . ."

--
Ted Bennett
Portland OR

Ted Bennett writes:

The flimsy perforated disks offered today are a mere lacework of
thin steel that is easily deformable at room temperature and
easily collapsible at yellow heat, which it would achieve on
descending roads I have encountered on my rides.

I've had a play on a MTB with discs and a sharp stop on level
ground from only about 15mph made the front disc too hot to touch.
There isn't much heat capacity because the manufacturers have to
keep the weight competitive with rim brakes.

However, I once saw a pair of (heavy looking) touring tandemists
who were solely relying on Hope discs front and rear; the discs
were rather blued by heat but the tandemists were satisfied with
their performance so far. They weren't as drilled-out as the
latest MTB types, but I'm sure they'd still get cherry red on a
serious descent. Maybe that's part of the fun.

Tandemists who follow consumer trends are already adopting disks.
The best setup would be double discs, as this would reduce,
practically to zero, torque caused by a solitary disk. And of
course a double would result in a much larger heat capacity.

I have seen a Phil Wood double-disk front hub, but I can't provide a
Web reference. Cost? "If you have to ask..."

That's interesting. I haven't see a left hand threaded hub or a left
hand threaded brake disc attachment. Who sells these and what do they
cost? Of course the main thing is to get a fork built that can
withstand brake torque at the dropout, something conventional road
forks do not do safely. The tandem riders I know have a rear disk to
take up excess speed achieved on straight runs and then use rim brakes
to control speed just before and in turns.

Yes, I have to ask.

Jobst Brandt

How high does the pressure have to get before a tire blows off? I
could try it by putting a couple of cartridges of CO2 in a wheel
but, for some reason, don't feel like it. Would a steel bead keep
it on better than a composite bead?

No. As I explained, the tire is held in place by the clinch, not the
constriction of the bead wire or Kevlar. Besides, All the tires I
have witnessed blowing off were steel beaded tires.


Some questions:

So why is a bead with high tensile strength needed at all? Why can't
the bead be pure rubber/casing material?


If I understand correctly the rubber bead becomes more 'slippery'.
Wouln't a more pronounced cinch on both tyre and rim overcome this?
Also, would a rough surface on the rim's cinch also help?


As I understand it, insulating rim strips are no longer available.
Would it be feasible to make some, or at least just out some
insulating material between a typical Velox tape and the rim.?
How about a strip of that white, woven (glass?) material used for
insulating parts in the engine bays of race cars work?
How about (quite a) few layers of plumber's PTFE tape?
How about putting ceramic coatings to good use and applying it the
inside of the U channel of a rim rather than the side walls (has it
been proven that these coating initiate cracks in the same manner as
hard-anodisation)?


How about tubes with built in over-pressure release valves? It would
seem to be a trivial modification that would not add significant
weight, or complexity.

Thanks,

Thomas Hood

wrote in message ...
Jay Beattie writes:

Sounds like an argument for disk brakes.

Interesting that you bring that up. I am unwilling to load my bicycle
with the extra weight and complexity to try it but I have considered
the heat I have observed. I cannot imagine that the typical disc we
see on bicycles today, weighing only a few 100 grams, can absorb the
energy required without collapsing and initiating brake failure. A
crumpled disk is a certain endo that I am unwilling to test, even if I
were offered such a bicycle before a descent.

The flimsy perforated disks offered today are a mere lacework of thin
steel that is easily deformable at room temperature and easily
collapsible at yellow heat, which it would achieve on descending roads
I have encountered on my rides.

In the summer:

http://tinyurl.com/pd86


When I first arrived in Colorado, I rather foolishly decided to go to
Winter Park, ski resort and take my bike up the ski lift and cycle
down. Now I considered myself to be a reasonably good MTB'er but
quickly found myself out of my depth; the trail being both extremely
steep and rocky (as in large rocks) After a semi-nasty fall, I lost my
nerve, and descended the rest of the slope v.slowly indeed. Definitely
slower than 10mph. My bike was equipped with hydraulic disk brakes:
Magura Julies. At no point did they fail, indeed my controlled descent
never required more than one finger.

Subsequently I've ridden the same trail at much higher speed as I
became more competent, with no problems. Now I'll happilly admit that
they look spindly, but I've never heard of disks collapsing as you
suggest, although a friend reports his XT disk brakes fade on this
run, but this is a pads issue I surmise. Has anyone heard of the disk
itself buckling (not just warping sligthly), and indeed actually seen
said item?

This may sound perverse, but I've knowingly tried to see if I could
get the rear disk to 'fade' but to no avail. I've tried this on
roads/trails that I believe are as steep as those to which you refer,
i.e 12% (cf. bottom part of Magnolia Rd, off Boulder Canyon).

I'm not averse to your supposition, but my practical experience has
not borne this out.

Thomas Hood



A couple of side-notes:

The disks on my bike are the standard stainless steel 180mm/190g front
and 160mm/155g rear. These seem to be significantly larger than most:
Shimano XT (2003 model without separate spider) are 160mm/140g FRONT!

I weigh 70kg.

On my descent at Winter Park they did ooze fluid out the reservoir as
they heated up to such an extent. Now the reason for this I believe is
that Magura and Shimano both use mineral oil, instead of DOT fluid. I
can't imagine that would have happened if DOT fluid had been specced.

I don't see the benefit of disks out in Colorado as there's no mud to
speak of, however in the UK they're the single best thing to have
happened to MTBs IMO; I'd never go back, to the massive drag of
clogged rims/brakes and the 'dissapearing' act that rims and pads do
in such conditions.